The present invention relates generally to structural testing and structural monitoring, and in particular to detecting the onset of structural failure by analysis of sample oscillation mode spectra.
Structural failure can be unpredictable and catastrophic, posing both financial risk and a threat to personal and public safety. Traditional destructive testing techniques are effective at determining a failure threshold, but cannot generally detect the onset of failure before it occurs. As a result, safety margins must be determined a priori or by trial and error.
This presents a significant problem for non-destructive testing, in which unanticipated structural failure can result in both economic loss and safety hazards. Post-testing failures (i.e., during construction or use) may be even more serious, but are even more difficult to predict.
Traditional structural inspection techniques suffer from limited accessibility and require significant time and expertise. This forces an economic tradeoff between the inspection cycle and its cost, resulting in inspections that are at best periodic, or that occur only after a significant event such as earthquake, fire, or accident. Moreover, traditional inspection techniques tend to rely on visual surveys which are quite different from the methods employed during structural testing. This makes correlation between the two approaches difficult, further compromising the ability of traditional structural testing and inspection to detect the onset of structural failure before it actually occurs.
Structural health monitoring (SHM) systems address some of these concerns. SHM systems employ a variety of sensing and measurement technology, utilizing generally small, remotely-operated sensors. These provide information on position, temperature, and other physical quantities, and allow for continuous monitoring in otherwise inaccessible locations. SHM systems may also employ active ultrasonic transducers to “interrogate” a structure or material, to detect displacement, delamination, cracking, or other local failures via the resulting change in Lamb wave transmissions.
Nonetheless prior art SHM utility remains limited because the systems do not apply the same monitoring techniques as those used during structural testing, and because the prior art cannot detect the onset of failure before it has occurred, at least on a local scale. There thus remains a need for a more integrated and forward-looking approach to structural testing and structural health monitoring.